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git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@6437 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
155 lines
3.4 KiB
C
Executable File
155 lines
3.4 KiB
C
Executable File
/* ENC.C - Encoding procedures. */
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/* Copyright (c) 1995-2012 by Radford M. Neal.
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*
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* Permission is granted for anyone to copy, use, modify, and distribute
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* these programs and accompanying documents for any purpose, provided
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* this copyright notice is retained and prominently displayed, and note
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* is made of any changes made to these programs. These programs and
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* documents are distributed without any warranty, express or implied.
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* As the programs were written for research purposes only, they have not
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* been tested to the degree that would be advisable in any important
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* application. All use of these programs is entirely at the user's own
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* risk.
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <math.h>
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#include "rand.h"
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#include "alloc.h"
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#include "mod2sparse.h"
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#include "mod2dense.h"
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#include "mod2convert.h"
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#include "rcode.h"
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#include "enc.h"
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/* The procedures in this module obtain the generator matrix to use for
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encoding from the global variables declared in rcode.h */
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/* ENCODE A BLOCK USING A SPARSE REPRESENTATION OF THE GENERATOR MATRIX. */
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void sparse_encode
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( char *sblk,
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char *cblk
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)
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{
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int i, j;
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mod2entry *e;
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char *x, *y;
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x = chk_alloc (M, sizeof *x);
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y = chk_alloc (M, sizeof *y);
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/* Multiply the vector of source bits by the systematic columns of the
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parity check matrix, giving x. Also copy these bits to the coded block. */
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for (i = 0; i<M; i++) x[i] = 0;
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for (j = M; j<N; j++)
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{
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cblk[cols[j]] = sblk[j-M];
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if (sblk[j-M]==1)
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{ for (e = mod2sparse_first_in_col(H,cols[j]);
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!mod2sparse_at_end(e);
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e = mod2sparse_next_in_col(e))
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{ x[mod2sparse_row(e)] ^= 1;
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}
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}
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}
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/* Solve Ly=x for y by forward substitution, then U(cblk)=y by backward
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substitution. */
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if (!mod2sparse_forward_sub(L,rows,x,y)
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|| !mod2sparse_backward_sub(U,cols,y,cblk))
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{
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abort(); /* Shouldn't occur, even if the parity check matrix has
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redundant rows */
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}
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free(x);
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free(y);
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}
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/* ENCODE A BLOCK USING DENSE REPRESENTATION OF GENERATOR MATRIX. */
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void dense_encode
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( char *sblk,
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char *cblk,
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mod2dense *u,
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mod2dense *v
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)
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{
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int j;
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/* Copy source bits to the systematic part of the coded block. */
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for (j = M; j<N; j++)
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{ cblk[cols[j]] = sblk[j-M];
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}
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/* Multiply by Inv(A) X B to produce check bits. */
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for (j = M; j<N; j++)
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{ mod2dense_set(u,j-M,0,sblk[j-M]);
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}
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mod2dense_multiply(G,u,v);
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/* Copy check bits to the right places in the coded block. */
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for (j = 0; j<M; j++)
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{ cblk[cols[j]] = mod2dense_get(v,j,0);
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}
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}
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/* ENCODE A BLOCK USING MIXED REPRESENTATION OF GENERATOR MATRIX. */
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void mixed_encode
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( char *sblk,
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char *cblk,
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mod2dense *u,
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mod2dense *v
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)
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{
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mod2entry *e;
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int j;
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/* Multiply the vector of source bits by the message bit columns of the
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parity check matrix. Also copy these bits to the coded block. Take
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account of how columns have been reordered. */
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mod2dense_clear(u);
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for (j = M; j<N; j++)
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{
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cblk[cols[j]] = sblk[j-M];
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if (sblk[j-M]==1)
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{ for (e = mod2sparse_first_in_col(H,cols[j]);
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!mod2sparse_at_end(e);
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e = mod2sparse_next_in_col(e))
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{ (void) mod2dense_flip(u,mod2sparse_row(e),0);
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}
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}
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}
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/* Multiply by Inv(A) to produce check bits. */
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mod2dense_multiply(G,u,v);
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/* Copy check bits to the right places in the coded block. */
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for (j = 0; j<M; j++)
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{ cblk[cols[j]] = mod2dense_get(v,j,0);
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}
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}
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